1. Field of the Invention
The present invention generally relates to diagnostic and test equipment for analyzing high-speed data bit streams and, more particularly, to devices and methods capable of measuring, among other things, the analog input performance of a high-speed data communications receiver.
2. Description of the Related Art
Frequency response is a common measure for diagnosing and analyzing a communication channel. Among other things, the frequency response of a communication channel defines the analog bandwidth that limits the channel capacity. Understanding the frequency response is a key element to diagnosing problems with individual devices and entire systems.
There exists presently commercial instruments known as network analyzers or vector network analyzers. These analyzers measure frequency response directly from the channel under test. These devices typically output sine waves at various frequencies and measure the sine wave power output from a device under test (DUT). The analyzer then is able to display the ratio of input power to output power versus frequency for the DUT.
It is known to build similar functionality from separate devices or instruments such as a synthesizer (sine wave generator) and an RF power meter for a more manual test. Power meters can be replaced with spectrum analyzers in this application, as well. The power meter then is capable of measuring the output power of the device. In all cases, the test system generates a sine wave of known amplitude and presents this to the DUT. Then the DUT outputs a sine wave back to the test system and the test system calculates and presents the ratio of output power to input power.
However, none of the aforementioned systems or analyzers truly tests the input frequency response of a decision circuit. For example, the goal of a decision circuit is to digitally sample the input signal and output a logical one or zero as a result of the decision. This is compatible with measuring the output of a sine wave for a power measurement to be measured by a power meter. Also decision circuit outputs are often highly integrated with other functions including serial to parallel shift registers that aggregate the binary decisions into multi-bit parallel words that, again, cannot be presented to a power meter for a power measurement.
There presently exists an urgent need to be able to measure the analog frequency response of the DUT, so that a proper measurement of that point of a digital receiver can be made. Thus, there still exists the need to be able to measure such digital receivers in transceiver devices and receiver-only devices.